The term "stent" is generally used to describe endoprothstetic medical devices which are implanted in anatomical passageways (e.g., blood vessels, gastrointestinal tract, genitourinary tract, endocrine ducts, etc. . . .) of the body for the purpose of maintaining the patency or state of dilation of the passageway, reinforcing the passageway, or anchoring a tubular graft or other object within the passageway.
Typically, such stents are implanted in blood vessels to maintain dilation and patency of an occluded region of blood vessel, or to bridge a weakened or aneurysmic region of blood vessel. On the other hand, some typical non-vascular applications of such stents are for the treatment of constrictions or injuries to the gastrointestinal tract (e.g., esophagus), ducts of the biliary tree (e.g., common bile duct) or anatomical passageways of the genitourinary tract (e.g., ureter, urethra fallopian tube, etc.).
Transluminally implantable stents are initially disposed in a compact configuration of relatively small diameter, and are initially mounted upon or within a delivery catheter to facilitate insertion and transluminal advancement of the stent into the desired anatomical passageway. Thereafter, such stents are radially expanded to a larger "operative" diameter which is equal to or slightly larger than the diameter of the anatomical passageway in which the stent is to be implanted. When radially expanded to such operative diameter, the stent will typically become released or separated from the delivery catheter and anchored or frictionally engaged to the surrounding wall of the anatomical passageway.
Some stents have a pliable, continuous tubular covering, in which case they are typically referred to as a "stented graft" or "stent-graft".
In general, stents and stented grafts fall into two major categories--a) self-expanding and b) pressure-expandable. Those of the self-expanding variety may be formed of resilient or shape memory material (e.g., spring steel or nitinol.TM.) which is capable of self-expanding from its first (radially compact) diameter to its second (operative) diameter without the exertion of outwardly-directed force against the stent or stented graft. Examples of such self-expanding stents and stented grafts are set forth in U.S. Pat. Nos. 4,655,771 (Wallsten, et al); 4,954,126 (Wallsten); 5,061,275 (Wallsten, et al); 4,580,568 (Gianturco); 4,830,003 (Wolf, et al); 5,035,706 (Gianturco, et al); 5,330,400 (Song) and 5,354,308 (Simon, et al) and Foreign Patent Publication Nos. WO94/12136; WO92/06734 and EPA183372. Those of the pressure-expandable (i.e., "passive expandable") variety may be formed of plastically deformable material (e.g., stainless steel) which is initially formed in its first (radially compact) diameter and remains stable in such first diameter until such time outwardly directed pressure is exerted upon the stent or stented graft to cause radial expansion and resultant plastic deformation of the stent or stented graft, to its second (operative) diameter. Examples of such pressure-expandable stents and stented grafts are set forth in U.S. Pat. Nos. 5,135,536 (Hillstead); 5,161,547 (Tower); 5,292,331 (Boneau); 5,304,200 (Spaulding); 4,733,665 (Palmaz); 5,282,823 (Schwartz, et al); 4,776,337 (Palmaz); and 5,403,341 (Solar) and Foreign Patent Publication Nos. EPA480667; and WO95/08966.
In many applications, careful positioning and sound anchoring of the stent or stented graft is critical to the successful treatment of the underlying medical problem. In this regard, the delivery catheter which is utilized to insert and position the stent or stented graft may be an important aspect of the overall system. Various types of delivery catheters for stents and stented grafts have been previously known, including those described in U.S. Pat. Nos. 4,665,918 (Garza, et al); 4,733,665 (Palmaz); 4,739,762 (Palmaz); 4,762,125 (Leiman, et al); ,776,337 (Palmaz); 4,838,269 (Robinson, et al); 4,994,071 (MacGregor); 5,037,427 (Harada, et al); 5,089,005 (Harada); 5,102,417 (Palmaz); 5,108,416 (Ryan, et al); 5,141,498 (Christian); 5,181,920 (Mueller, et al); 5,195,984 (Schatz); 5,201,901 (Harada, et al); 5,269,763 (Boehmer, et al); 5,275,622 (Lazarus, et al); 5,290,295 (Querals, et al); 5,306,294 (Winston, et al); 5,318,588 (Horzewski, et al); 5,344,426 (Lau, et al); 5,350,363 (Goode, et al); 5,360,401 (Turnland); 5,391,172 (Williams, et al); 5,397,345 (Lazarus); 5,405,380 (Gianotti, et al); 5,443,452 (Hart, et al); 5,453,090 (Martinez, et al); 5,456,284 (Ryan, et al); and 5,456,694 (Marin, et al) and Foreign Patent Publication Nos. EP-0308-815-A2; EP-0335-341-A1; EP-364-787-A; EP-0442-657-A2; EP-482976-A; EP-0505-686-A1; EP-0611-556-A1; EP-0638-290-A1; WO94/15549; WO95/01761; GB2196-857-A; DE3042-229; and DE3737-121-A.
As previously indicated, many types of stents or stented grafts are currently used in relation to the treatment of various disorders. Perhaps the most common use of radially expandable stents and stented grafts is in relation to the treatment of narrowed or constricted blood vessels. For these applications, pressure expandable stents are typically employed, with the delivery of the stent to the desired treatment site being facilitated through the use of a delivery catheter including an inflatable balloon which is used to facilitate the radial expansion of the stent positioned thereupon to its final, operative diameter.
When using pressure expandable stents or stented grafts on a delivery catheter including an inflatable balloon, the stent or stented graft must be manually mounted to the balloon of the delivery catheter by the physician prior to the initiation of the treatment. Such mounting is typically accomplished by the physician manually squeezing or compressing the stent or stented graft onto the balloon of the delivery catheter. It is also known in the prior art for delivery catheters to be provided wherein the stent or stented graft is pre-mounted thereto. In this respect, the stent or stented graft is mounted to the delivery catheter by the manufacturer, and sold as a combined unit.
Though the above-described mounting procedure is often used, a major drawback associated therewith is that often times the stent or stented graft is not uniformly compressed onto the balloon of the delivery catheter. Indeed, the hand crimping of the stent or stented graft onto the balloon of the delivery catheter usually results in uneven crimping. Such non-uniform or uneven crimping of the stent or stented graft onto the balloon in turn results in non-uniform or uneven re-expansion of the stent or stented graft when radially expanded by the inflation of the balloon. If re-expanded in a non-uniform manner, the stent or stented graft, though being in contact with the luminal surface of a particular anatomical passageway, will not necessarily exert even pressure thereagainst, which is undesirable due to the increased risk of the stent or stented graft dislodging from its operative position within the treatment site. Additionally, such non-uniform crimping may cause problems during the advancement of the delivery catheter through the anatomical passageway to the desired treatment site. Such problems include those portions of the stent or stented graft which are not compressed against the balloon of the delivery catheter inadvertently contacting and damaging the lining of the luminal surface of the anatomical passageway.
In view of the foregoing, it is highly desirable to facilitate the uniform crimping or compression of the stent or stented graft over the balloon of the delivery catheter. The present invention addresses this need by providing an apparatus and method which, through the use of hydraulics, facilitates the uniform radial compression of the stent or stented graft about a portion of the delivery catheter. The present invention is used primarily in relation to pressure expandable stents or stented grafts which are mounted to the balloon of a delivery catheter. However, the present invention may also be used in relation to self-expanding stents or stented grafts including a latching mechanism which engages when the stent or stented graft is radially compressed.